Methods currently exist for introducing cloned copies of genes into the mouse germ line to form transgenic mice. Recent studies indicate that under appropriate conditions introduced genes exhibit regulated expression characteristic of the endogenous genes. Moreover, methods are available for making defined modifications to cloned genes in vitro. Reintroduction of such modified genes into inbred mice affords novel opportunities for studying gene function and dissecting the mechanisms regulating complex gene interactions, such as those which typify physiologic homeostases, in higher animals. We propose to use such an approach to address issues pertinent to mammalian blood pressure regulation. In initial studies, we will use modified forms of renin structural gene and regulatory sequences in attempts to perturb normal physiological functions in inbred mice. Subsequently we plan to extend our studies to include other genetic components that contribute to blood pressure regulation and electrolyte balance. The initial types of modifications we will make are aimed at 1) overproducing natural murine renin at normal sites of synthesis, 2) placing renin synthesis under the control of regulatory elements that are insensitive to and independent of normal blood pressure physiologic signals, 3) producing renin polypeptides that are impaired or altered at catalytic sites and/or cellular processing and activation signals, and 4) transforming renin producing cells in situ using renin regulatory sequences fused to oncogenes. The effects of such perturbations will be monitored by directly assessing at various levels the expression of the inserted gene, the response of other known components of the regulatory network, and whole animal physiological parameters such as, for example, blood pressure and heart rate. Animals exhibiting interesting properties will then be bred to establish lines which will be available for continued study. Over the long term such in vitro mutagenesis coupled with a mammalian system that is readily manipulated genetically affords the best hope of establishing animal model systems for molecular genetic analysis of complex mechanisms governing physiological regulation in higher animals.